The present invention relates generally to a sealing arrangement for a bucket cooling circuit in a gas turbine engine. More particularly the present invention relates to a conformable seal design that is responsive to centrifugal force to seal between a turbine rotor spacer and the axial end faces of a turbine rotor wheel and bucket dovetails of a heavy duty gas turbine engine in order to minimize leakage of bucket cooling air.
Due to high operating temperatures in gas turbine engines it is common to convectively cool one or more stages of turbine buckets to improve durability. Typically the cooling air is bled from one or more stages of the compressor and is passed to the turbine rotor through various passages that may consist of multiple interfacing parts. The air bled from the compressor is higher in pressure than the air in the turbine and thus each interface poses a potential leak path for the cooling air. One such leak path is the interface between the rotor spacer and the rotor wheelposts and bucket dovetails.
Several methods have been previously employed to seal this type of leak path. In turbines for use as aircraft engines, cover plates (or blade retainers) are installed on the forward and aft sides of the bucket/wheel end faces and have wire seals across the interrupted faces. See, for example, U.S. Pat. Nos. 4,500,098 and 5,622,475. The cover plates serve to seal in cooling air provided the airfoils and also hold the buckets in place axially. Though the seal works well, serviceability of the turbine becomes an issue since replacement of one or more of the buckets requires disassembly of the rotor. Heavy duty land based turbines on the other hand must have the capability to replace buckets in the field. In prior heavy duty turbine designs, there is typically a cylindrical axial protrusion on the spacer rim that has a interference fit (rabbet) with the underside of the wheel rim. A tangential slot is cut into the underside of the wheel rim that penetrates into the dovetail slot. The penetration allows cooling air to pass from the spacer/wheel cavity into the bucket, the rabbet fit between the wheel and spacer rim acting as a seal. A separate hook on the wheel and bucket in combination with a retaining ring holds the bucket axially in place. While this design enables the bucket to be removed in the field, the design results in undesirable stress concentrations in the wheel rim.
Consequently, there has developed a need for a seal assembly which will minimize or eliminate stress concentrations on the wheel, provide an effective seal for cooling air entering the bucket airfoil via the space between the spacer and the wheel and prevent ingestion of hot gas from the gas path into the cooling air flow path.